In the fields of wellbore construction and intervention, swellable tools are used to provide isolation between two regions in an annulus formed between an exterior surface of a tubular and an interior surface of well casing or a wellbore. A swellable member is formed from an elastomeric material selected to swell when placed in certain fluids. Where the swellable member swells in oil, the member may comprise ethylene propylene diene monomer rubber (EPDM). Where the swellable member swells in water, the member may comprise an N-vinylcarboxylic acid amide-base cross-linked resin and a water swellable urethane in an ethylene-propylene rubber matrix.
Applications of swellable tools are limited by a number of factors including: their capacity for swelling, their ability to create a seal, and their mechanical properties when in their unexpanded and expanded states. Swellable packers, for example, may be exposed to high pressure differentials across the packer. The integrity of the annular seal created by a well packer is paramount, and extrusion or deformation of the expanding portion will result in a potential failure mode between the apparatus and the bore wall. In practice therefore, swellable tools are designed to take account of the limitations of the materials. For example, a swellable packer may be run with an outer diameter only slightly smaller than the borehole, to limit the percentage volume increase of the swellable material during expansion. In addition, swellable packers may tend to be long compared with mechanical or hydraulic isolation tools in order to the pressure rating and/or reduce the chances of breach in the seal at high differential pressures.